Of course the Lib Dems don't want House of Lords reform – they just want to keep their constituency boundaries

Two years ago, David Cameron's Conservative Party, up against the most unpopular prime minister in recent history, at the height of economic collapse that the public widely held the Labour Party responsible for, failed to win a majority in Parliament. That simple fact ought to be repeated at every political strategy meeting in No 10 Downing Street and CCHQ. If the Tories couldn't win in 2010, how on earth are they meant to increase their tally in 2015?

One of the answers was meant to be boundary reform. The Conservatives tend to suffer from our electoral system, for two reasons. First, Tory constituencies are usually larger in population than Labour ones – the result of years of migration from cities to the countryside. Second, voters in rural Tory constituencies are more likely to turn out than their urban peers, so Tory MPs pile up enormous majorities which aren't matched elsewhere.

Boundary reform deals with the first of those problems, by resizing all constituencies to approximately 76,000 voters (about the current size of David Cameron's constituency of Witney, coincidentally). That should give the Conservatives about a 20 seat boost in the next election.

Should – except that it's widely thought that it won't happen. This morning, Richard Reeves, Nick Clegg's outgoing adviser, has given an interview to the Independent, in which he confirms what everybody thought: the Liberal Democrats will block the boundary reforms – which are due to pass through Parliament next year – if House of Lords reform is blocked by Conservative rebels.

Superficially, it looks like a threat – back down, or you won't get your majority. But actually, it's the opposite – it's an open invite for many Tories to rebel.

For those who wonder why the Lib Dems are pushing House of Lords reform so aggressively, here is your answer. It's nothing to do with principle, or even to do with securing jobs for MPs who lose at the next election. Rather, it's about leverage – because the Lib Dems really don't want boundary reform. The party's strength is based on years – decades even – of constituency level campaigning, and boundary reform threatens to undo all that. Prominent Lib Dem MPs, including Tim Farron, Vince Cable and Simon Hughes, are all threatened by the changes. The inevitable failure of House of Lords reform is an excuse to back down from such a self-destructive commitment.

And lots of Tory MPs will support them – by using the excuse of opposing Lords reforms, they actually get to act in self-interest against party interest. A Conservative majority is only worth fighting for if you are sure to be a part of it after all, and for MPs like Nadine Dorries, whose Mid Bedfordshire seat is to be abolished, boundary reform is career destroying. As a Tory source pointed out to me this morning, as many as half of the 40 Group – the Tory MPs in the forty most marginal seats – are threatened by the review. They won't all vote in the party interest.

Thanks to that, David Cameron will keep pushing House of Lords reform, even though personally, he thinks it is a "third term issue". He knows that without it, the chances of his winning a Conservative majority in 2015 are minimal. So much for Government in the national interest.